DOCSLIB.ORG

International Society for Soil Mechanics and Geotechnical Engineering

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
International Society for Soil Mechanics and Geotechnical Engineering INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. The paper was published in the proceedings of the 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering and was edited by Prof. Denis Kalumba. The conference was held in Cape Town, South Africa, on October 07-09 2019. Proceedings of the 17th African Regional Conference on Soil Mechanics and Geotechnical Engineering. 7, 8 & 9 October 2019 – Cape Town The limitations of standpipe piezometers in stability analysis L. Geldenhuys, Y. Narainsamy & F. Hörtkorn Jones & Wagener, Johannesburg, South Africa ABSTRACT: The pore pressure regime, material strength parameters and geometry of a Tailings Storage Fa- cility (TSF) influence the stability, often expressed as a Factor of Safety (FoS). Of these variables it is the pore pressure that is the likely to change in temporal and spatial variance within a relatively short period of time and which will have a significant impact on the FoS of the facility. Standpipe piezometers are often used in South Africa to monitor pore pressures within a TSF. Analyses were conducted to compare the FoS calculated for non-hydrostatic spatial distributions of pore pressures and the FoS calculated for sketched phreatic levels and hydrostatic conditions. Phreatic levels were from water levels in hypothetic standpipe piezometers that would measure pore pressures in the reference model. The FoS values calculated showed that the FoS for the models with pore pressures from the sketched phreatic levels under hydrostatic conditions were non-conservative. This highlights the need for alternative methods, such as regular piezocone probing, to determine the pore pressures in a TSF for stability monitoring. 1 INTRODUCTION Of these, it is the pore pressure regime that is most likely to vary rapidly throughout the lifetime of the Tailings Storage Facilities (TSFs) are used to store TSF and will affect a change in the Factor of Safety mine waste residue. The properties of this waste ma- (FoS) against failure. This paper aims to highlight the terial are generally related to the parent rock from influence that estimating the phreatic level from which it is being mined as well as the process method standpipe piezometers and assuming hydrostatic con- used to extract minerals. If the production process ditions can have on the calculated FoS compared to does not change, and the material is from a single when the FoS is calculated with the actual pore pres- plant, it is unlikely that the tailings material properties sures that are non-hydrostatic. The scope is limited to will change in a short period of time. an idealized gold TSF in which the material proper- Irrespective, the material properties will vary spa- ties are homogeneous. tially within the TSF due to segregation during depo- sition. Piezocone testing has been proven to be an ef- fective method to determine the material properties in 2 PORE PRESSURES WITHIN A TSF the TSF. Hydraulic deposition is the primary deposition The seepage and pore pressure regime within a TSF method used in South Africa. The residue is deposited can have spatial and temporal variation and is in slurry form and, as it settles and consolidates, ex- influenced by deposition cycles and deposition cess water is returned to the plant to be re-used. This control, rainfall, decanting procedures, drainage is predominantly through decanting structures. A net- conditions, facility height, base geometry, work of drains can be implemented to collect some of consolidation, etc. Recently, the increase in the the interstitial water. The interstitial water, the expul- number of lined facilities, due to the promulgation of sion of excess water due to consolidation and the as- more stringent environmental legislation in South sociated flow to the drains or decant structure result Africa, has resulted in the assumptions regarding in a pore pressure distribution within the TSF that drainage conditions having to be reconsidered. The may vary spatially. flow conditions are three-dimensional, temporally The material properties and spatial distribution, variable and are therefore complicated to predict. TSF geometry as well as the pore pressure distribu- Pore pressures are often measured in a TSF as an tion within a TSF control the stability of the TSF input parameter to conduct regular stability analyses. (Wagener et al. 1998). The pore pressures can be determined by conducting 435 17th ARC Conference 2019 Cone Penetration Testing with pore pressure (considering the flow regime) while the dashed line measurements (CPTu) probing, also referred to as represents the phreatic surface inferred from the piezocone probing. piezometer measurements without considering the Although this provides an accurate representation flow regime. Note that, although the pore pressures of the pore pressure in the TSF (Wagener et al., 1998), indicated by the piezometers are correct, the inferred the costs associated with conducting these tests and phreatic surface is below the true phreatic surface. the fact that the results are only representative for the time (therefore also the dam geometry) at which probing was done warrants that alternative solutions are required to measure pore pressures at shorter intervals. In order to obtain continuous data for monitoring, permanent fixture devices are installed to indicate pore pressures in a TSF. In South Africa, the pore pressures are traditionally measured using open-end standpipe piezometers and vibrating wire piezometers. Both measure pore pressure at a specific depth below the surface and, to effectively use the measured data, the reference elevation of these depths needs to be known. Other devices, such as twin-tube hydraulic piezometers, porous piezometers, Figure 1. Difference in true phreatic level and piezometer level pneumatic piezometers and electrical resistance (Blight 2010) piezometers (among others) are available to the industry (Ridley et al. 2003). Although available, not all these methods are implemented. 3 METHOD AND ANALYSIS The open-end standpipe piezometer is the most commonly used in the experience of the authors and 3.1 Scope consists of a filter at the end of tube or pipe that is The scope of this paper is limited to the comparison extended to the surface. The piezometer will normally of the FoS calculated with phreatic levels inferred be installed in the centre of a drill hole, the end filled from standpipe piezometers and hydrostatic with wet sand (adjacent to the porous filter) and the conditions and the FoS calculated with pore pressures remainder of the gap around the pipe (above the from CPTu testing for stability analysis on a TSF. The porous filter) will be grouted closed. Because of this analysis was conducted by calculating the FoS using installation technique, the water level in the standpipe limit equilibrium slope stability analysis (method of only responds to the water pressure at the bottom of slices according to Morgenstern-Price, 1965) for the the standpipe and is isolated from other pore pressure outer wall of an idealised TSF with typical material regimes along the length of the standpipe. The water parameters for gold tailings. The material parameters level in the standpipe is therefore a measure of the used are summarised in Table 1. equipotential at the tip and, as such, the water level in The model geometry and phreatic lines considered a standpipe will rise to the potential at the bottom of are shown in Figure 2 and are based on typical TSFs the standpipe. assessed by the authors. The assignment of the mate- The seepage regime within a TSF seldomly results rial regions as well as the bench dimensions are in hydrostatic pore pressure conditions, particularly shown in Figure 3. The analysis was repeated for the towards the outer wall of the facility where flow lines case of a starter wall. This was done to force the slip are directed to underdrains. A flow gradient of surfaces to be above the bottom of the standpipes, 7 kPa/m has been considered to indicate drainage is based on the assumption that the starter wall is con- occurring (Vermeulen 2001) at that section and/or a structed with a material with a higher shear strength permeable foundation. Due to non-hydrostatic than the surrounding tailings. conditions there is often a difference between the water level within a standpipe piezometer and the true Table 1. Summary of material parameters phreatic level in the region where the standpipe is Material Unit weight Friction Cohesion installed. A piezometer will therefore give a false (kN/m3) angle (°) (kPa) phreatic level if the rate of pore pressure increase with Tailings 18 33 0 Base 22 40 0 depth is not hydrostatic. The magnitude of this Foundation 22 33 5 difference is associated to the depth to which a Starter wall 22 40 0 standpipe is installed and the rate of pore pressure increase with depth. This difference is depicted in Figure 1. The upper, solid line of the flownet represents the true phreatic surface within the TSF 436 L. Geldenhuys, Y. Narainsamy & F. Hörtkorn was done to have a representation of various failure mechanisms. These analyses formed a single analysis set. The analysis set (Case A, B and C for each of Case 1, 2 and 3) was then repeated for the model with a starter wall (Fig. 3). Once all the critical FoS values for the reference case were determined, the analysis was then repeated, only this time the pore water pressure in the model was derived by drawing in the phreatic surface and Figure 2.
Load more

Recommended publications
  • Instrumentation for Monitoring Consolidation of Soft Soil 1
    ONE STOP MONITORING SOLUTIONS | HYDROLOGY | GEOTECHNICAL | STRUCTURAL | GEODETIC Over 50 years of excellence through ingenuity APPLICATION NOTE INSTRUMENTATION FOR MONITORING CONSOLIDATION OF SOFT SOIL 1. Introduction Considerable settlement may occur when constructing projects such as highway embankments, bridge approaches, dikes, dams, large storage areas, tanks, airport runways or buildings on soft compressible soil, due to the consolidation of soil under the superimposed load. To avoid serious and potentially expensive problems due to such settlement, it is desirable to cause the consolidation to occur at the outset of the project, and in the shortest possible time during construction period. Construction of a facility on top of a soft soil foundation will normally be delayed until there is assurance that it will not be damaged by settlement that occurs during subsequent consolidation. If the predicted delay is not acceptable, the time required for consolidation can be reduced by surcharging and/or by installation of vertical drains. 1.1 Consolidation In case a saturated soil experiences a steady pressure due to the weight of overlying soil or pre-loading from an embankment, its volume will decrease with time. Soil particles as well as the water in the voids being almost incompressible at the pressures encountered, any change in volume can only occur if the water between the voids is forced out. This reduces the size of the voids enabling the solid particles to become wedged closer together. The process is illustrated in figures 1.1 and 1.2 below: Im posed Stress h W a t e r Figure 1.1 Im posed Stress h W a t e r Figure 1.2 Surcharging (or pre-loading) involves placement of fill materials to a level higher than that required for the foundation or embankment, so that consolidation proceeds more quickly.
    [Show full text]
  • Piezometer Installation 2017
    Revision 2016-1-1 Copyright ©, 2016 by HMA Group. The information contained in this document is subject to change without prior notice. Contents 1. Introduction:................................................................................................................................................................ 3 2. Specifications: ............................................................................................................................................................. 4 3. Vibrating Wire Piezometer Operation .............................................................................................................. 5 4. Calibration and Interpreting Readings ............................................................................................................. 6 4.1 Electrical Connection ............................................................................................................................................. 6 4.2 Calibration Sheet Interpretation ...................................................................................................................... 7 4.3 Data Reduction ......................................................................................................................................................... 8 4.4 Pressure Head/Water Level Calculation ....................................................................................................... 9 4.5 Barometric Compensation .................................................................................................................................
    [Show full text]
  • Method 9100: Saturated Hydraulic Conductivity, Saturated Leachate
    METHOD 9100 SATURATED HYDRAULIC CONDUCTIVITY, SATURATED LEACHATE CONDUCTIVITY, AND INTRINSIC PERMEABILITY 1.0 INTRODUCTION 1.1 Scope and Application: This section presents methods available to hydrogeologists and and geotechnical engineers for determining the saturated hydraulic conductivity of earth materials and conductivity of soil liners to leachate, as outlined by the Part 264 permitting rules for hazardous-waste disposal facilities. In addition, a general technique to determine intrinsic permeability is provided. A cross reference between the applicable part of the RCRA Guidance Documents and associated Part 264 Standards and these test methods is provided by Table A. 1.1.1 Part 264 Subpart F establishes standards for ground water quality monitoring and environmental performance. To demonstrate compliance with these standards, a permit applicant must have knowledge of certain aspects of the hydrogeology at the disposal facility, such as hydraulic conductivity, in order to determine the compliance point and monitoring well locations and in order to develop remedial action plans when necessary. 1.1.2 In this report, the laboratory and field methods that are considered the most appropriate to meeting the requirements of Part 264 are given in sufficient detail to provide an experienced hydrogeologist or geotechnical engineer with the methodology required to conduct the tests. Additional laboratory and field methods that may be applicable under certain conditions are included by providing references to standard texts and scientific journals. 1.1.3 Included in this report are descriptions of field methods considered appropriate for estimating saturated hydraulic conductivity by single well or borehole tests. The determination of hydraulic conductivity by pumping or injection tests is not included because the latter are considered appropriate for well field design purposes but may not be appropriate for economically evaluating hydraulic conductivity for the purposes set forth in Part 264 Subpart F.
    [Show full text]
  • 2 Basic Concepts and Definitions
    2 Basic concepts and definitions This chapter summarises some basic concepts and definitions of terms rele- vant to the hydraulic properties of water-bearing layers and the discussions which follow. 2.1 Types of water-bearing layers Water-bearing layers are classified according to their water-transmitting properties into aquifers, aquitards or aquicludes. With regard to the flow to pumped wells the following definitions are commonly used. -An aquifer is a water-bearing layer in which the vertical flow component is so small with respect to the horizontal flow component that it can be neg- lected. The groundwater flow in an aquifer is assumed to be predominantly horizontal. -An aquitard is a water-bearing layer in which the horizontal flow compo- nent is so small with respect to the vertical flow component that it can be neglected. The groundwater flow in an aquitard is assumed to be predomi- nantly vertical. - An aquiclude is a water-bearing layer in which both the horizontal and ver- tical flow components are so small that they can be neglected. The ground- water flow in an aquiclude is assumed to be zero. Common aquifers are geological formations of unconsolidated sand and gravel, sandstone, limestone, and severely fractured volcanic and crystalline rocks. Examples of common aquitards are clays, shales, loam, and silt. 2.2 Aquifer types The four types of aquifer distinguished (Figure 2.1) are: confined, unconfined, leaky and multi-layered. A confined aquifer is a completely saturated aquifer bounded above and below by aquicludes. The pressure of the water in confined aquifers is usually higher than atmospheric pressure, which is why when a well is bored into the aquifer the water rises up the well tube, to a level higher than the aquifer (Figure 2.1.A).
    [Show full text]
  • Installing Monitoring Wells in Soils Version 1.0 August 2008
    Installing Monitoring Wells in Soils Version 1.0 August 2008 USDA – Natural Resources Conservation Service National Soil Survey Center Lincoln, Nebraska Correct document citation: Sprecher, S.W. 2008. Installing monitoring wells in soils (Version 1.0). National Soil Survey Center, Natural Resources Conservation Service, USDA, Lincoln, NE. Cover Figure: Schematic diagram of a standard design for an installed water-table monitoring well. Use of trade or firm names is for reader information only, and does not constitute endorsement or recommended use by the U.S. Department of Agriculture of any commercial product or service. The United State Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at 202-720-2600 (Voice and TDD). To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washington, D.C. 20250 or call 1-800-245-6340 (voice) or (202) 720-1127 (TDD). USDA is an equal employment opportunity employer. Acknowledgements This technical note is a compilation of concepts and procedures that have been evolving within pedology and Soil Survey for at least three decades. Few of the ideas presented originated with myself. It is an honor to recognize and thank my main teachers concerning these procedures, Lawson Smith (US Army Engineer Waterways Experiment Station, Vicksburg, Mississippi, deceased) and Jim Richardson (North Dakota State University and NRCS National Soil Survey Center in Lincoln, Nebraska, retired).
    [Show full text]
  • Hvorslev (1951)
    TIME LAG AND SOIL PERMEABILITY IN GROUND-WATER OBSERVATIONS BULLETIN NO. 36 WATERWAYS EXPERIMENT STATION CORPS OF ENGINEERS, U. S. ARMY VICKSBURG, MISSISSIPPI TIME LAG AND SOIL PERMEABILITY IN GROUND-WATER OBSERVATIONS BULLETIN NO. 36 WATERWAYS EXPERIMENT STATION CORPS OF ENGINEERS, U. S. ARMY VICKSBURG, MISSISSIPPI APRIL 1951 ARMY - MRC VICKSBURG, MISS. 111 CONTENTS Page PREFACE . i ACKNOWLEDGEMENTS. ii NOTATION. v INTRODUCTION . 1 PART I: GROUND-WATER CONDITIONS AND OBSERVATIONS Irregularities and Variations. 3 Sources of Error in Measurements. 3 Hydrostatic time lag. 4 Stress adjustment time lag. 4 General instrument errors. 4 Seepage along conduits . 4 Interface of liquids. .. 6 Gas bubbles in open systems . 6 Gas bubbles in closed systems . 6 Gas bubbles in soil. 7 Sedimentation and clogging. 7 Erosion and development. 7 Summary comments . 8 PART II: THEORY OF TIME LAG The Basic Hydrostatic Time Lag . 9 Applications for Constant Ground-Water Pressure. 10 Applications for Linearly Changing Pressures . 13 Applications for Sinusoidal Fluctuating Pressures. 16 Corrections for Influence of the Hydrostatic Time Lag. 19 Influence of the Stress Adjustment Time Lag . 21 Initial disturbance and stress changes . 22 Transient consolidation or swelling of soil . 23 Volume changes of gas in soil . 26 Normal operating conditions. 28 iv CONTENTS (Cont’d) Page PART III: DATA FOR PRACTICAL DETERMINATION AND USE OF TIME LAG Flow through Intakes and Well Points . 30 Influence of Anisotropic Permeability . 32 Computation of Time Lag for Design Purposes . 35 Examples of Field Observations and Their Evaluation . 38 Logan International Airport, Boston. 38 Vicinity of Vicksburg, Mississippi. 39 Determination of Permeability of Soil in Situ .
    [Show full text]
  • Geotechnical Bulletin
    Ohio Department of Transportation Division of Production Management Office of Geotechnical Engineering GB 4 Geotechnical Bulletin GUIDELINES FOR THE USE OF GEOTECHNICAL INSTRUMENTATION May 30, 2008 Geotechnical Bulletin GB4 was developed by the Office of Geotechnical Engineering. This document is the first edition. This Geotechnical Bulletin is intended to provide information about the uses of the various different geotechnical instruments that are available so that designers will prescribe them whenever beneficial and so that construction personnel will utilize them properly. More specifically, this geotechnical bulletin is intended to offer guidance in terms of when exactly these instruments should be called for, which instruments should be prescribed, where to install them, how to read them and how to interpret and utilize the data. Geotechnical instruments can measure conditions in the subsurface and acquire data which can greatly aid not only the designer, but also the project engineer and the contractor. The designer benefits from this data which can help them pinpoint the problems in the subsurface and thereby design an appropriate and cost effective project. In terms of the construction of the project, although these instruments can get in the way of the heavy equipment, they provide data that is invaluable in terms of preventing a possible failure during or following construction as well as allowing the construction to proceed at the earliest possible date whenever waiting periods are necessary. Another important reason to use instrumentation is to monitor for any unsafe conditions and therefore to try to prevent an accident or injury. For example, monitoring a mine subsidence site may tell us at what point a highway facility is no longer safe and needs to be shut down.
    [Show full text]
  • Techniques of Backfiguring Consolidation Parameters from Field Data
    TRANSPORTATION RESEARCH RECORD 1277 71 Techniques of Backfiguring Consolidation Parameters from Field Data RICHARD p. LONG Methods of analyzing field consolidation data from areas with Field consolidation data must be analyzed by some theory. and without vertical drains are presented. All methods analyze The analytical procedures presented here are based on the field data independently of laboratory data. Settlement data from small strain theory of Terzaghi (1). The limitations of this areas having vertical drains can be analyzed by three different theory are well known, but it provides useful information techniques to yield values of the apparent coefficient of consol­ idation and the ultimate settlement for foundation clay. Analysis because, for most soft soils capable of supporting a fill, Ter­ of piezometer data yields values of apparent coefficient of con­ zaghi's theory is a good approximation. For the case of vertical solidation by a separate technique. Data from areas without drains drains, Barron's modification using equal strain consolidation can be analyzed for similar parameters. All methods involve the is used (2), rather than the direct extension of Terzaghi's use of Terzaghi's theory of consolidation or Barron's equal strain theory by free strain. theory for areas with vertical drains. These theories are appro­ Although the analysis process may be considered an autopsy priate for analysis of most clay deposits. The techniques are illus­ trated and results from their use on the consolidation of varved (3), progress in geotechnical engineering, as in medicine, clay beneath the approach fills of the Putnam Bridge are pre­ advances by the judicious use of the autopsy.
    [Show full text]
  • Preliminary Results of Subsurface Exploration and Monitoring at the Johnson Creek Landslide, Lincoln County, Oregon
    Preliminary Results of Subsurface Exploration and Monitoring at the Johnson Creek Landslide, Lincoln County, Oregon Open-File Report 2007-1127 U.S. Department of the Interior U.S. Geological Survey Preliminary Results of Subsurface Exploration and Monitoring at the Johnson Creek Landslide, Lincoln County, Oregon By William H. Schulz and William L. Ellis Open-File Report 2007-1127 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia: 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Schulz, W.H., and Ellis, W.L., 2007, Preliminary results of subsurface exploration and monitoring at the Johnson Creek landslide, Lincoln County, Oregon: U.S. Geological Survey Open-File Report 2007-1127, 11 p., 1 appendix. iii Contents Abstract ...........................................................................................................................................................1
    [Show full text]
  • Landslides and Slope Stability
    _ LANDSLIDES AND SLOPE STABILITY APPLICATION NOTES _EN_05_02/2016 _EN_05_02/2016 LANDSLIDES LANDSLIDES AND SLOPE STABILITY _EN_05_02/2016 “The term “landslide” describes a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill, or a combination of these.” (USGS, 2004). LANDSLIDE A change in the stability of a slope can be caused by a number of factors, acting together or alone, natural (groundwater pressure, toe erosion, earthquake, etc...) or occurring with human activities (blasting, excavations, constructions, etc...) Instrumentation in landslides usually monitors not only the body of the landslide, but also the buildings in the area, the protective structures, the weather parameters and, if needed, seismic parameters. LANDSLIDE TYPES AIMS • Rotational landslide • Landslide early warning system (EWS) • Translational landslide • Monitoring of buildings • Lateral slide in or nearby landslide areas • Rockfall • Railway and road safety • Topple • Monitoring performance • Debris flow of protective structures www.sisgeo.com LANDSLIDE AND SLOPES STABILITY 2 EXAMPLE OF ROTATIONAL LANDSLIDE MONITORING _EN_05_02/2016 _EN_05_02/2016 INSTRUMENT PURPOSE Wire crackmeter Monitoring of cracks in rock masses or ground displacement LANDSLIDES Vented pressure transducer Measurement of water level in standpipe piezometer Digital MEMS in-place Monitoring of deep lateral movements inclinometers in sliding areas Standpipe piezometer Utilized to measure water table with water
    [Show full text]
  • Measurement of Groundwater Table & Pore Water Pressure in Deep
    KMS / TECHNICAL DEPARTMENT TECHNICAL NOTE 008 Measurement of Groundwater Table & Pore Water Pressure In Deep Excavations · We excel through experience and learning · Version 02, Jul 2013 Keywords blockage at the outlet. This will lead to a build-up of water Perforated standpipe, standpipe piezometer, groundwater table, pressure, and the water head H2 will become higher than the groundwater movement, excess pore water pressure, hydrostatic head. hydraulic instability Now that if a manometer is placed inside a water tank (with an orifice), the following scenarios can be observed. Synopsis In deep excavations, it is imperative to understand the (i) (iii) (ii) effectiveness of water cut-off provided by the cofferdam walls and/or toe grouting, and also the groundwater movement and pore water pressure both inside and outside the cofferdam. The latter is of particular importance because the build-up of excess pore water pressure on the passive side (excavation side) of the cofferdam walls could lead to hydraulic instability of the cofferdam owing to piping. Water flow 1.0 Introduction Prior to discussing the measurement of groundwater table, pore water pressure, and its relevance to deep excavation, it is perhaps useful to look at the following water In location (i), which is far from the orifice, the water flow flow scenarios and the respective water head measured by a velocity is relatively slow and water is in a near-static condition. manometer. The water level measured by the manometer will practically be the same as the water level in the tank. Whereas in location (ii), which is adjacent to the orifice, water flows at much higher (a) (b) (c) velocity.
    [Show full text]
  • Instrumentation Practice for Slope Monitoring
    Submitted for Publication in: "ENGINEERING GEOLOGY PRACTICE IN NORTHERN CALIFORNIA" Association of Engineering Geologists INSTRUMENTATION PRACTICE FOR SLOPE MONITORING William F. Kane President and Principal Engineer KANE GeoTech, Inc. P.O. Box 7526 Stockton, CA 95267-0526 Timothy J. Beck Associate Engineering Geologist California Department of Transportation Transportation Laboratory 5900 Folsom Boulevard P.O. Box 19128-0128 Sacramento, CA 95819 ABSTRACT Remote monitoring of slope movement using electronic instrumentation can be an effective approach for many unstable or potentially unstable slopes. Water levels can be observed using vibrating wire piezometers. Movements and deformation can be determined with electrolytic bubble “in-place” inclinometers and tiltmeters, extensometers, and time domain reflectometry (TDR). All of these instruments can be attached to a programmed on-site datalogger. The datalogger can collect readings at selected intervals and trigger an alarm or initiate a telephone message or page if pre-determined movement intervals are exceeded. These systems are self-contained using cellular telephone communications and batteries charged by solar panels. Case studies in Central and Northern California illustrate the use and flexibility of this technology in monitoring slope stability problems. INTRODUCTION Many options are available for monitoring unstable, and potentially unstable, slopes. These range from inexpensive, short-term solutions to more costly, long-term monitoring programs. The remote location of many unstable slopes has created a need for systems that can be accessed remotely and provide immediate warning in case of failure. Advances in electronic instrumentation and telecommunications now make it possible to monitor these slopes economically. Kane and Beck - 1/20 Slope stability and landslide monitoring involves selecting certain parameters and observing how they change with time.
    [Show full text]